The interaction of silver foil with oxygen over a wide range of temperatures and O2 pressures has been studied by XPS, TPD, and TPR. It has been shown that depending on the treatment conditions two adsorbed oxygen states with a different ionicity of the Ag-O bond can be formed, as well as oxygen dissolved in the silver bulk. "Ionic" oxygen [E(b)(O 1s) = 528.4 eV] is formed in the initial step of O2 adsorption, its incorporation into uppermost silver layer proceeding at T > 420 K. This state is responsible for ethylene adsorption, followed by its destruction and complete oxidation to CO2 and H2O. Dissolution of oxygen atoms in the silver bulk starts at T > 470 K. No effect of the dissolved oxygen on the electronic and catalytic properties of the "ionic" oxygen has been revealed. Accumulation of "covalent" oxygen [E(b) (O 1s = 530.5 eV] occurs at higher temperature and pressure. A possible mechanism for its formation which includes the creation of specific defective sites on silver surface is discussed. Despite a large variation of pressures and temperatures used for the modification of clean silver foil by O2, all attempts to produce a surface active in ethylene epoxidation have failed.